Binder for coating composition

ABSTRACT

A binder for a coating composition is obtainable as the reaction product of a carboxyl-terminated fatty acid ester with an ethylenically unsaturated carboxylic acid and an ethylenically unsaturated carboxylic acid ester. The carboxylic fatty acid ester is produced by reaction of an autoxidisable fatty acid and a polyol, with modification to introduce at least one terminal carboxyl group. The reaction is optionally effected in an organic solvent which is substantially removed at the end. The material is neutralized with a base to render it water-soluble. Thixotropy can be endowed by an amine/(poly)isocyanate final reaction stage to prior neutralization.

FIELD OF INVENTION

The present invention relates to a water-reducible binder for use inaqueous structured coating compositions such as paints and lacquers.

BACKGROUND

Solvent borne air drying coatings have been used on substrates such aswood and metal for many years. Generally, they are used both to giveprotection to the substrate and to provide an aesthetically pleasingappearance. Depending upon the nature of the polymeric binder used inthe final coating, these decorative air drying coatings can be appliedto both interior and exterior surfaces.

For both consumer and professional applications, the predominant organicsolvent is conventionally an aliphatic hydrocarbon such as white spirit,which contains around 18% aromatic materials. More recently, whitespirit has been replaced with low aromatic analogues which have thebenefit of reducing the toxicity of the solvent and at the same time,reducing odour. Other organic solvents such as esters and ketones areoften present in small quantities, usually from such additives asdriers, fungicides and tinters.

Despite the move towards less toxic and lower odour solvents, the factthat organic solvents are used, still results in their evaporation intothe atmosphere after application, thus contributing to atmosphericpollution.

A reduction in the level of volatile organic solvents used in decorativecoatings is therefore considered desirable, indeed necessary. Thedevelopment of high solids paints, with much lower levels of organicsolvent, would have a significant impact on atmospheric pollution.However, the introduction of such products has been delayed due to thelack of enforcing legislation and their relatively higher price.

An alternative to the organic solvent as a mobile carrier for the resin,pigment etc., is water. Water based decorative coatings have beenavailable for many years and the most common types are generallyformulated on thermoplastic (co)polymers derived from monomers such asvinyl acetate, vinyl acetate/Veova, vinyl acetate/ethylene copolymers,styrene, styrene/methacrylates. In these cases, the polymer is formed byemulsion polymerisation in the aqueous phase, to produce an emulsionwith dispersed discrete particles. Polymers formed by this processusually have a very high molecular weight. In order for coatings to beformed from these polymers, the particles must coalesce to form acoherent resistant film. Due to the nature of the polymerisationprocess, water sensitive materials remain in the thermoplastic coating.

Air drying water borne resins have also been available for many years.These may be alkyds with high acid value. Traditionally, this acidityhas been achieved by ring opening of trimellitic anhydride by reactionwith a hydroxyl terminated alkyd. The alkyd may then be thinned to about70% to 80% in a water miscible organic solvent such as butyl glycol andneutralized with ammonia or amine, to render the product waterdilutable. These materials have never achieved commercial success in thedecorative paint market, due to high solvent content and poorapplication and performance properties.

Alkyd emulsions are another route to producing water based decorativecoatings. It is reasonable to assume that these will retain theiroxidative nature and so crosslink after application. However, they havenot gained a large commercial success in decorative paints andvarnishes, due to performance related problems, such as yellowing,drying, drier stability, water resistance and poor rheology.

Therefore, there is still a need for an autoxidisable binder forwater-based coatings which can produce finished coatings with higherabrasion resistance and/or hardness, are preferably also faster-dryingand in the case of the known high-acid resins, contain less organicsolvent.

One preferred sub-class of binders according to the invention comprisesthose which result in thixotropic coating compositions. Therefore, it isconvenient here to review the prior art relating to thixotropic system.

The solvent based coatings widely used in the domestic consumer marketare generally thixotropic in appearance. That is to say that the paintexhibits time dependent recovery. In the undisturbed state at low shearrates, these coatings, which can be paints, varnishes or stains, have ahigh apparent viscosity. The actual low shear viscosity will depend uponthe degree of structure in the coating but in a typical non-drip coatingthe low shear viscosity would be in the order of 1 000 000 mPa.s. Thishas the effect of making the coating appear like a jelly in theindisturbed state in the can before application. At high shear rates,typically those experienced when the paint is brushed out, the paintwill exhibit the viscosity characteristics of a liquid paint thusallowing easy application. Once brushing is stopped, the paints willshow a recovery in viscosity and structure with time. This will allowthe paints to flow and level on the substrate without sagging, thusgiving a coating which is uniform in thickness and virtually free frombrush marks.

This thixotropic character can conveniently be measured using a constantstress rheometer and undertaking an oscillation recovery sweep. Theparameters measured are the elastic modulus G′ and the viscous modulusG″. Immediately after applying a shearing force, the viscous moduluswill dominate and the paint will flow. As time passes, both G′ and G″show an increase. With a thixotropic material, the rate of increase inthe elastic modulus will be faster than G″ and will eventually overtakethe viscous modulus, at which time the product can be considered to bemore solid in nature and will now no longer sag.

Any product which after a period of time after applying a shearing forcewill show a curve in which G′ increases at a faster rate than G″ can beconsidered thixotropic.

The truly thixotropic solvent based coatings, widely available in thedomestic consumer market, are usually based on autoxidisable binderswhich have been chemically modified by polyamide technology orurethane/urea technology as described in GB-A-1,454,388 andGB-A-1,454,414.

Other known means of imparting structure into solvent based coatings,which is not truly thixotropic, is by means of clays, silicas, amideadditives, hydrogenated castor oil additives.

The water based binders described above, whether they are thethermoplastic emulsion (co)polymers or alkyd emulsions, which are widelyused in the domestic decorative market, are not inherently thixotropic.Any structure, which these materials have, is imparted by the additionof additives at the paint manufacturing stage and not by chemicalmodification of the binder itself.

There have been other proposals for thixotropic systems which areaqueous, for example utilising the binder disclosed in GB-A-2,237,576.It is based on an acrylic polymer having hydroxyl and carboxylic acidpendant groups. This polymer material is made thixotropic by reactionwith an isocyanate having at least two isocyanate groups, an aminehaving at least two amino groups and a primary or secondary monoamine.However, although these polymers are water-dispersed, their ability topost-cure, and therefore their final film performance is limited.

Thus, to date, there remains a need for a commercially viable waterbased coating system and in particular, a binder therefore, which systemcan be produced in thixotropic or non-thixotropic form as required.

SUMMARY OF INVENTION

The present invention now provides a binder for a water-based coatingcomposition, the binder being obtainable as the product of a reactionmixture comprising:

a) a carboxy-terminated fatty acid ester obtainable as the reactionproduct of an autoxidisable fatty acid and a polyol followed by areaction to attach a carboxy group,

b) an ethylenically unsaturated carboxylic acid, and

c) an ester of an ethylenically unsaturated carboxylic acid.

Binders according to the present invention, are suitable forincorporation in water borne coating compositions such as (depending onthe particular binder in question) paints, lacquers, varnishes orstains.

In its broadest definition, the present invention encompasses bindersfor water-borne coatings which result in non-thixotropic compositions,those which result in thixotropic compositions and those which areprecursors (i.e. capable of conversion to) binders which result inthixotropy. Moreover, the binders of any of the aforementioned classesmay in themselves be provided in neutralized form, ready for use in themanufacture of coating compositions or in un-neutralized form forneutralization by the manufacturer. The invention also encompassescoating compositions containing any of these compositions.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENT OF THE INVENTION

The binders of the present invention render the final compositionair-drying because they are obtained from an autoxidisable fatty acidwhich has been esterified with a polyol and then terminated with acarboxy group.

Binders according to the present invention, whether or not for producingthixotropy when incorporated in the final coating product, confer one ormore advantages in performance in comparison with water-bornecompositions based on conventional binders. These advantages areselected from one or more at higher abrasion resistance, increasedhardness, faster drying and the need for less organic solvent in thefinal reaction mixture.

However, coatings intended for application other than as floor coatingsrequire some degree of rheological control to provide adequateapplication properties in terms of flow, leveling and sag control. Thisis normally achieved in solvent based coatings by the use of thixotropicbinders or by the use of thixotropic additives which are added duringthe paint manufacturing process.

Preferably, in order to provide a water based thixotropic coating,binders according to the present invention are modified such that theybecome thixotropic (i.e. confer thixotropy in the final coatingcompositions) without the use of other external additives. In theseinstances, the resulting products will not necessarily be truly watersoluble.

This modification to provide thixotropy in the final product is obtainedby making a precursor material which is obtainable when a hydroxyfunctional monomer material is included in the reaction mixture withreactants (a), (b) and (c). The precursor is then converted to athixotropic binder by reaction with at least one amine, followed byreaction with an isocyanate material.

Water reducibility of the final product can be achieved by neutralizingwith an appropriate base, for example one or more materials selectedfrom ammonia, primary, secondary and tertiary amines and alkali metalhydroxide. Suitable amines include triethylamine, diisopropylamine,triethanolamine, dimethylethanolamine and morpholine.

Regarding starting materials, modified autoxidisable fatty acids areknown. Typical autoxidisable fatty acids are the unsaturated fatty acidswhich are known as “drying oils” and are found in various mixtures innatural substances such as soya bean oil, sunflower oil or saffloweroil, e.g. oleic, linoleic and linoleic acids. For example,9,12-octadecanoic acid is a constituent of soya bean oil and sunfloweroil. Those acids having at least two double bonds, having no methylenelinkage therebetween (i.e. the conjugated fatty acids) are preferred forfaster drying. Most useful examples have from 15 to 24 carbon atoms. Thecarboxyl-terminated polyol esters of these acids are convenientlyprepared by a first reaction stage, starting with the fatty acid and apolyhydric alcohol. The fatty acid ester undergoes a second stage ofreaction to yield the carboxy-terminated fatty acid ester whichpreferably contributes from 20% to 80% of the weight of the resultantbinder, whether unmodified or in the neutralized and/or thixotropicallymodified forms which will be explained in more detail hereinbelow.

Preferably, the first-stage (uncarboxylated) fatty acid ester is formedby reacting fatty acids with polyhydric alcohols at eg. 200° to 250° C.to an acid number of between 0 and 10 mgKOH/g, preferably to less than 5mgKOH/g.

Suitable vegetable oil fatty acids include non-conjugated, conjugated ormixtures of both. Suitable examples of non-conjugated acids includelinoleic acid, linolenic acid, tall oil fatty acids, linseed fattyacids, soya bean fatty acids, and sunflower fatty acids. Suitableexamples of conjugated fatty acids include dehydrated castor oil fattyacid, the UKD products supplied by Henkel such as UKD3510 and UKD6010and the Unichema products PRIFAC7967 and 7968.

The fatty acid is esterified with one or more polyhydric alcohols whichcontains two or more hydroxyl groups per molecule. Typical examplesinclude 1,6-hexane diol, glycerol, trimethylol propane, pentaerythritol,di-trimethylol propane and di-pentaerythritol.

The resultant fatty acid ester contains an excess of hydroxyl groups,preferably yielding a product with a hydroxyl number of between 10 and100 mgKOH/g preferably between 20 and 70 mgKOH/g.

After reaction, of the fatty acid and the polyol, a subsequent reactionis effected to attach at least one carboxylic acid group. This isconveniently effected by reaction with a carboxylic acid anhydride suchas trimellitic anhydride (TMA), maleic anhydride, phthalic anhydride,tetrahydrophthalic anhydride, or pyromellitic anhydride, or a mixture ofany two or more thereof. The final acid value of the thus carboxylatedfatty acid ester is from 10 to 100 and preferably from 20 to 70 mgKOH/g.

In a preferred embodiment of this first stage of reaction, the fattyacids and polyols are charged to the reactor and heated to a maximum of250° C., removing water until the acid number falls to less than 10mgKOH/g, preferably to less than 5 mgKOH/g. The resultant fatty acidester is then cooled to 170° C. and TMA is added. The mixture is held at170° C. until ring opening of the TMA has occurred, yielding a productwith an acid value of between 10 and 100 mgKOH/g preferably between 20and 70 mgKOH/g.

The next stage of the process is then to copolymerise the ethylenicallyunsaturated acid and ester monomers in the presence of thecarboxy-terminated fatty acid ester. These monomers preferably compriseacrylic acid and/or methacrylic acid together with one or more esters ofacrylic acid and/or one or more esters of methacrylic acid.

Suitable esters of acrylic or methacrylic acids are those containing1-12 carbon atoms such as methyl (meth)acrylate, butyl (meth)acrylate,isobutyl (meth)acrylate, ethyl (meth)acrylate, ethyl hexyl acrylate,glycidyl (meth)acrylate, hydroxyethyl (meth)acrylate and hydroxypropyl(meth)acrylate. Preferred examples are methyl methacrylate, butylmethacrylate, butyl acrylate, hydroxy ethyl methacrylate and methacrylicacid mixed in the appropriate ratios. Preferably, an “equivalent”polymer formed only by polymerisation of reactants (b) and (c) andoptionally, any additional ethylenically unsaturated monomer(s) (seebelow) in the same amounts as in the binder according to the presentinvention has a glass transition temperature of from 263° K. to 373° K.,preferably from 273° K. to 343° K.

It is necessary to employ both the ethylenically unsaturated carboxylicacid and the ester of an unsaturated carboxylic acid. The former isnecessary to incorporate the required acid functionality. The latter isnecessary to ensure the hardness of the final coating. The ester doesnot necessarily have to be an ester of the same ethylenicallyunsaturated acid which is incorporated in the form of acid per se.Mixtures of different acids and/or different esters could be employed.In general, the ratio of acid to ester is preferably from 0.1:1 to0.22:1 by weight.

It is also preferred to include in the reaction mixture with thecarboxyl-terminated fatty acid ester, the ethylenically unsaturatedcarboxylic acid and the ester of an ethylenically unsaturated carboxylicacid, an additional ethylenically unsaturated monomer componentcomprising one or more suitable ethylenically unsaturated monomers suchas vinyl toluene or styrene or one of its derivatives (such as α-methylstyrene). Of course, mixtures of such other unsaturated monomers mayalso be used. These additional unsaturated monomers can provideadditional benefits such as hardness and durability.

The selection of the particular monomers for the mixture overall,depends on a number of factors but especially on the polymer's finalapplication and performance requirements, including the aforementionedacid number of 20 to 75 mgKOH/g, but most preferably 35 to 70, to allowfor neutralization, prior to dilution in water.

This reaction is preferably carried-out in the presence of an organicsolvent in order to facilitate the manufacture and handleability of thefinished product, before dilution with water. The choice of organicsolvent for this stage can be a water miscible solvent, which will stillbe present, and in fact will be required to be in, the final neutralizedand water thinned resin. Alternatively, the solvent for this stage maybe one which simply acts as a medium for the addition polymerisation andwhich will be removed after this stage of the process. In this case, anaddition of a water-miscible co-solvent will be required beforeneutralizing and dilution with water.

In any event, it is preferred that the solvent (if used) in this stagedoes not contain any labile hydroxyl groups, as these will esterify withthe carboxyl groups present in the monomer mixture and/or the fatty acidester. Where a hydroxyl containing solvent is used in the final product,then a non reactive solvent such as xylene or toluene can be used, thisthen being removed after the addition polymerisation.

When the addition of the carboxylic acid group (e.g. by a ring openingreaction with a corresponding anhydride) is complete, the product iscooled to a suitable temperature. This temperature is determined by thenature of the carrier solvent and the choice of polymerisation catalyst.Preferably, the solvent is added to a level of 20 to 50%, calculated onthe weight of the overall reaction mixture.

In a typical reaction, a mixture consisting of ethylenically unsaturatedester and acid monomers is prepared and a polymerisation catalyst isalso added. Preferably, this mixture is added to the carboxy-terminatedfatty ester solution over a period of 2 to 8 hours. Typically, thetemperature of the reaction can be between 70° C. and 170° C.,preferably between 110° C. and 140° C.

Typical polymerisation catalysts are di-tertiary butyl peroxide,tertiary butyl perbenzoate, tertiary butyl octoate, di-tertiary-amylperoxide, dicumyl peroxide and 1,1 bis (tertiary butyl peroxy)cyclohexane.

After the monomers have been added, the resin is preferably held ontemperature until polymerisation is complete. If necessary, furtheradditions of polymerisation catalyst can be made, to ensure completeconversion.

When the reaction is complete, a part of the process solvent is removed,preferably by vacuum distillation. If the processing solvent is the sameas that desired in the final resin, then enough is removed to give a nonvolatile content (NVC) of from 70 to 95% by weight, preferably from 75to 95%. If an intermediate processing solvent, such as xylene, is used,then substantially all of this is removed, and the preferred watermiscible solvent is added to give a non volatile content of from 70 to95%, preferably from 75 to 95% by weight resin. For avoidance of doubt,in the context of the present invention, the term “substantially allremoved” means that afterwards, the non volatile content of the mixtureis more than 90% by weight, preferably more than 95% by weight, andespecially more than 98% by weight. Suitable examples of water misciblesolvents include any alcohol, glycol ether, glycol ether ester or amixture of such solvents. Examples are, but not limited to, propan-1-ol,propan-2-ol, butan-1-ol, butan-2-ol, butyl glycol, propylene glycol,propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether, propylene glycol dimethyl ether and N-methyl pyrrolidone.

Water reducibility can be conferred by the neutralization of the resinbefore addition of water as hereinbefore described. This is effected byadding ammonia or amines such as triethylamine, diisopropylaminetriethanolamine, dimethylethanolamine or morpholine.

As mentioned above, to induce thixotropy in the final product, aprecursor is made by including a hydroxy functional material in thereaction mixture of (a), (b) and (c) and this precursor is then reactedwith at least one amine (preferably a monoamine or diamine or mixturethereof followed by reaction with at least one isocyanate (either amonofunctional or polyfunctional isocyanate or mixture thereof).

In a preferred embodiment, the precursor resin in solution (preferablyin an organic solvent) is warmed and then reacted preferably with amixture of mono and diamines. Further reaction of the amine salts soproduced is then undertaken by the introduction of polyisocyanatecontaining materials. Upon complete reaction of the amine groups,further amine is added to react with the residual carboxylic acid groupsof the polymer. Finally, the reaction mixture is diluted with water togive a water dispersible thixotropically modified binder.

Examples of suitable mono and diamines include (but are not restrictedto) ammonia, diethylamine, triethylamine, morpholine, 4-ethylmorpholine, ethanolamine, dimethyl amino propylamine, diethanolamine,methyl diethanolamine, ethylene diamine, hexamethylene diamine andm-xylene diamine.

Examples suitable of suitable monofunctional isocyanates include (butare not restricted to) methyl-, ethyl-, cyclohexyl- andphenyl-isocyanates and the reaction product of toluene diisocyanate anda monofunctional alcohol such as ethanol, butanol, cyclohexanol,tridecanol or butyl glycol.

Suitable polyfunctional polyisocyanate materials include (but are notrestricted to) isophorone diisocyanate, tolylene 2,4 diisocyanate,tolylene 2,6 diisocyanate, diphenyl methane diisocyanate, hexamethylenediisocyanate, proprietary material such as the dimer of hexamethylenediisocyanate sold as Tolonate HDB and a trimer of hexamethylenediisocyanate sold as Tolonate HDT both produced by Rhone Poulenc.

It is desirable to have a slight excess of amine over the isocyanategroups. The ratio of isocyanate to amine groups may for example be from0.9:1 to 1:0.9 but it is preferably less than or equal to 1:1.

The resins produced can be converted to coatings by the addition ofpigments, extenders, driers, fungicides, antioxidants and otheradditives that are well known in the industry. The resins described canalso be converted to clear varnishes.

The present invention will now be explained in more detail by way of thefollowing non-limiting examples.

EXAMPLES Example 1

A fatty acid ester was made by reacting 130.8 parts of sunflower fattyacid and 32.7 parts of Prifac 8960, a conjugated fatty acid availablefrom Unichema, with 41.8 parts of di-trimethylol propane. The mixturewas heated slowly to 240° C. and water removed until the acid number wasless than 4 mgKOH/g. The fatty acid ester was cooled to 170° C. and 13.2parts of trimellitic anhydride was added. The mixture was held at 170°C. for 30 minutes then cooled to 140° C. 379.0 parts of dipropyleneglycol dimethyl ether was added and the temperature held at 140° C.

A mixture of 47.3 parts of methacrylic acid, 181.8 parts of methylmethacrylate, 131.3 parts of butyl methacrylate, 25.4 parts of butylacrylate and 16.7 parts of tertiary-butyl perbenzoate was prepared andadded to the fatty ester over 3-4 hours. When all of the monomer mixturehad been added, the product was held at 140° C. for a further fourhours.

Vacuum was applied and the solvent removed until the non volatilecontent was higher 80% by weight. Vacuum was released and the resindiluted to 75.3% NVC with butyl glycol. The product was cooled anddischarged. It had a colour of 5 Gardner, a viscosity at 25° C. of143,300 mPa.s, a non volatile content of 75.3% and an acid number of65.7 mgKOH/g.

The product was neutralized with diisopropylamine and diluted to 30% nonvolatile content with water, to give a clear solution. Suitable driers(Combi LS) were added to give a final clear lacquer with an NVC of30.2%, viscosity of 300 mPa.s at 25° C. and a pH of 10. A film of thislacquer had a sand dry time of 30 minutes and was through dry in 1 hour,to give a coating with a Koening hardness of 14.4% after 1 day, 18.0%after 7 days and a 60° gloss of 90%.

Example 2

A fatty acid ester was made by reacting 122.4 parts of sunflower fattyacid and 30.6 parts of conjugated fatty acid Prifac 8960, with 39.1parts of di-trimethylol propane. The mixture was heated slowly to 240°C. and water was removed until the acid number was less than 4 mgKOH/g.This fatty acid ester was cooled to 170° C. and 12.4 parts oftrimellitic anhydride was added. The mixture was held at 170° C. for 30minutes then cooled to 138° C. 354.9 parts of xylene was added and thetemperature held at 138° C.

A mixture of 44.3 parts of methacrylic acid, 122.4 parts of methylmethacrylate, 123.1 parts of butyl methacrylate, 71.6 parts of butylacrylate and 15.6 parts of tertiary-butyl perbenzoate was prepared andadded to the fatty ester over 3-4 hours. When all of the monomer mixturehad been added, the product was held at 138° C. for a further fourhours.

Vacuum was then applied and the xylene removed until the non volatilecontent was higher than 98%. Vacuum was released and the resin dilutedto 90% NVC with butyl glycol. The product was cooled and discharged. Ithad a colour of 5 Gardner, a viscosity at 100° C. of 3,050 mPa.s, a nonvolatile content of 90.1% and an acid number of 59.1 mgKOH/g.

The product was neutralized with ammonia and diluted with water to givea clear solution. Suitable driers (Combi LS) were added to give a finalclear lacquer with an NVC of 25.9%, a viscosity of 80 mPa.s at 25° C.and a pH of 9.1. A film of this lacquer had a sand dry time of 24minutes and was through-dry within 7 hours to give a coating with aKoening Hardness of 6.9% after 1 day, 10.6% after 7 days and a 60° glossof 89%.

Example 3

A fatty acid ester was made by reacting 135.5 parts of Tall Oil fattyacid and 33.9 parts of conjugated fatty acid Prifac 8960, with 23.6parts of pentaerythritol. The mixture was heated slowly to 240° C. andwater was removed until the acid number was less than 4 mgKOH/g. Thisfatty acid ester was cooled to 170° C. and 12.4 parts of trimelliticanhydride added. The mixture was held at 170° C. and 12.4 parts oftrimellitic anhydride added. The mixture was held at 170° C. for 30minutes then cooled to 138° C.

354.4 parts of xylene was added and the temperature held at 138° C.

A mixture of 44.2 parts of methacrylic acid, 122.3 parts of methylmethacrylate, 123.0 parts of butyl methacrylate, 71.6 parts of butylacrylate and 15.6 parts of tertiary-butyl perbenzoate was prepared andadded to the fatty ester over 3-4 hours. When all of the monomer mixturehad been added, the product was held at 138° C. for a further fourhours.

Vacuum was applied and the xylene removed until the non volatile contentwas higher than 98%. Vacuum was released and the resin diluted to 90%NVC with butyl glycol. The product was cooled and discharged. It had acolour of 6 Gardner, a non volatile content of 89.8% and an acid numberof 61.0 mgKOH/g.

This resin was converted to a coating using the following formulation:

Resin at 89.8% solids 55.5 Water 40.0 Ammonia solution (35%) 4.5Bayowett 448 0.25 Combi LS (driers) 1.0 Methyl ethyl ketoxime 0.25 Water90

The resin was heated to 50° C. and the premixed water/ammonia, also at50° C., was added until the resin was neutralized to pH 8.5-9.0, atwhich time the solution became clear. The remaining components wereadded under slow stirring conditions, with the final amount of waterbeing added to give shear viscosity of 200 mPa.s at 10,000 sec⁻¹.

A film cast from this solution had sand dry time of 50 minutes, a harddry time of 4 hours. There was no evidence of tack after 24 hours dryingand the film had excellent gloss and water resistance.

Example 4

A fatty acid ester was made by reacting 113.9 parts of sunflower fattyacid and 28.5 parts of conjugated fatty acid Prifac 8960, with 36.3parts of di-trimethylol propane. The mixture was heated slowly to 240°C. and water removed until the acid number was less than 4 mgKOH/g. Thisfatty acid ester was cooled to 170° C. and 11.5 parts of trimelliticanhydride added. The mixture was held at 170° C. for 30 minutes thencooled to 138° C.

330.0 parts of xylene was added and the temperature held at 138° C.

A mixture of 25.8 parts of methacrylic acid, 113.8 parts of methylmethacrylate, 114.4 parts of butyl methacrylate, 66.6 parts of butylacrylate, 15.3 parts of hydroxy ethyl methacrylate and 14.5 parts oftertiary-butyl perbenzoate was prepared and added to the fatty esterover 3-4 hours. When all of the monomer mixture had been added, theproduct was held at 138° C. for a further four hours.

Vacuum was applied and the xylene removed, until the non volatilecontent was higher than 98%. Vacuum was released and the resin dilutedto 80% NVC with butyl glycol. The product was cooled and discharged. Ithad a colour of 3 Gardner, a non volatile content of 79.8% and an acidnumber of 45.5 mgKOH/g.

The resin was converted to a coating using the following formulation:

Resin at 79.8% solids 62.5 Water 40.0 Ammonia solution (35%) 4.1Bayowett 448 0.25 Combin LS (driers) 1.0 Methyl ethyl ketoxime 0.25Water 90

The resin was heated to 50° C. and the premixed water/ammonia, also at50° C. was added, until the resin was neutralized to pH 8.5-9.0, atwhich time the solution became clear. The remaining components wereadded under slow stirring conditions, with the final amount of waterbeing added to give a high shear viscosity of 200 mPa.s at 10,000 sec⁻¹.

A film cast from this solution had sand dry time of 1 hour 10 minutes, ahard dry time of 4 hours 15 minutes. There was no evidence of tack after24 hours drying and the film had excellent gloss and water resistance.

The above procedure was repeated, but the ammonia solution was replacedwith 3.2 g di-isopropylamine. A clear varnish was obtained, but uponapplication, the sand dry and hard dry times were extended to 5 hoursand 12 hours respectively. The cast film still showed some tack afterovernight drying and had inferior water resistance.

Example 5

85.1 parts of the resin solution from Example 4 (80% in butyl glycol)were heated to 50° C. 2.021 parts of morpholine were added and themixture stirred for 10 minutes, after which time 0.59 parts of ethylenediamine were added. After a further 10 minutes period of stirring at 50°C., 7.50 parts of Tolonate HDT were added. The mixture was held at 50°C. for 30 minutes to allow reaction of the amine. 4.789 parts ofmorpholine were then stirred in for 10 minutes. Finally, water at 50° C.was slowly added with stirring to give a water dispersible thixotropicbinder with a solids content of 40% and a pH-9.

Apart from the obvious presence of thixotropy as noted visually,thixotropy was also verified by determining a preshear oscillationrecovery curve in which it was observed that the elastic component G′after a period of 800 seconds dominates the viscous component G″.

Example 6

80 parts of the binder from Example 4 diluted in 80% NVC in dipropyleneglycol dimethyl ether were heated to 50° C. 1 part of xylene diamine wasadded and the mixture stirred for 10 minutes, after which time 6.3 partsof a tridecanol/TDI adduct was added and the mixture stirred for afurther 10 minutes. 4.4 parts of morpholine was added and the mixturestirred. Finally, 140 parts of water @ 50° C. was added slowly withstirring to give a water reducible thixotropic binder with a solidscontent of 31.4%.

What is claimed is:
 1. A binder for a water-based coating composition,the binder comprising the product of a reaction mixture consistingessentially of: (a) a carboxy-terminated fatty acid ester, obtained byreaction in two successive stages: a first stage where a fatty acidester is formed by reacting autoxidisable fatty acids with polyhydricpolyols at 200° C. to 250° C. to an acid number of less than 10 mg ofKOH/g and with the resultant fatty acid ester having an hydroxyl numberof between 10 and 100 mg KOH/g a second stage with reaction of the fattyacid ester of the first stage with a carboxylic acid anhydride at atemperature lower than that of the first stage to obtain thecarboxy-terminated fatty acid ester, with an acid value of between 10and 100 mg KOH/g; (b) an ethylenically unsaturated carboxylic acid; (c)an ester of an ethylenically unsaturated carboxylic acid, (d)optionally, an ethylenically unsaturated monomer, other than anethylenically unsaturated carboxylic acid, and (e) optionally, ahydroxyl functional monomer material.
 2. A binder according to claim 1,wherein an ethylenically unsaturated monomer, other than anethylenically unsaturated carboxylic acid, is also included in thereaction mixture.
 3. A binder according to claim 2, wherein anequivalent polymer, formed only from polymerization of reactants (b) and(c) and the ethylenically unsaturated monomer, has a glass transitiontemperature of from 263° K. to 373° K.
 4. A binder according to claim 3,wherein the equivalent polymer has a glass transition temperature offrom 273° K. to 343° K.
 5. A binder according to claim 2, wherein thereaction mixture further includes an organic solvent.
 6. A binderaccording to claim 1, wherein a hydroxyl functional monomer material isalso included in the reaction mixture.
 7. A thixotropic bindercomprising the reaction product of a binder according to claim 6, withat least one amine, followed by reaction with an isocyanate material. 8.A binder according to claim 6, wherein the reaction mixture furtherincludes an organic solvent.
 9. A binder according to claim 1, whereinthe reaction mixture is reacted in the presence of an organic solvent.10. A binder according to claim 9, wherein the organic solvent issubstantially removed after completion of the reaction.
 11. A binderaccording to claim 1, in which an equivalent polymer formed only frompolymerisation of reactants (b) and (c) has a glass transitiontemperature of from 263° K. to 373° K.
 12. A binder according to claim11, wherein the equivalent polymer has a glass transition temperature offrom 273° K. to 343° K.
 13. A binder according to claim 1, having afinal acid number of from 20 to 75 mgKOH/g.
 14. The binder according toclaim 8, having an acid number of from 35 to 70 mgKOH/g.
 15. A binderaccording to claim 1, wherein the reaction mixture further includes from20% to 50% by weight of organic solvent based on the weight of thereaction mixture.
 16. A binder according to claim 12, wherein the fattyacid is a non-conjugated acid or a conjugated acid, or a mixture ofnon-conjugated and conjugated acids.
 17. A binder according to claim 1,wherein the carboxylated fatty acid ester contributes from 20% to 80% byweight of the binder.
 18. A binder obtainable by neutralizing the binderaccording to claim
 1. 19. A coating composition comprising a binderaccording to claim 18, and water.
 20. A binder according to claim 1,wherein the fatty acid and polyol are reacted to an acid number of lessthan 5 mgKOH/g.
 21. A process for producing a binder for a water-basedcoating composition, the process comprising the steps of: (a) reactingan autoxidisable fatty acid and a polyol; (b) reacting the product of(a) with a carboxyl containing organic compound to attach a carboxylgroup; (c) introducing an ethylenically unsaturated carboxylic acid andan ester of an ethylenically unsaturated carboxylic acid to the reactionproduct of (b); and (d) reacting the combination of (c) to obtain thebinder.
 22. The process of claim 21, wherein an ethylenicallyunsaturated monomer other than an ethylenically unsaturated carboxylicacid, is introduced to the reaction mixture in step (c).
 23. The processof claim 21, wherein the reaction further comprises an organic solvent.